Efficient Degradation of Bezafibrate Using the Fe(II)/Sulfite Process: Kinetics, Mechanism and Influence on DBP Formation

Bezafibrate (BZF), an extensively used lipid-regulating agent, has been frequently detected in aqueous environments. In this work, we systematically investigated the Fe(II)/sulfite process for degrading BZF and its impact on disinfection byproducts (DBPs) during postchlorination. Degradation conditions were optimized by adjusting the pH, sulfite concentration, Fe(II), and BZF concentration. Under the conditions of pH = 4, [BZF]₀ = 5 μM, [Fe(II)]₀ = 25 μM, and [sulfite]₀ = 250 μM, the BZF removal efficiency reaches 97.9% in 15 min. Sulfate radicals (SO₄^●–) and singlet oxygen (¹O₂) are recognized as the main reactive agents, with Fe(IV) also contributing to the removal of BZF. Common anions (Cl⁻ and HCO₃⁻) and humic acid generally impede the degradation process, except that trace amounts of Cl⁻ can slightly accelerate BZF degradation. A total of ten products are recognized by ultra high performance liquid chromatography and quadrupole time-of-flight mass spectrometry, and four major degradation pathways are proposed: hydroxylation, cleavage of amino bonds, removal of fibrate chains, and dechlorination. Meanwhile, the toxicity assessment shows that the majority of products exhibit lower biological toxicity and less bioaccumulation potential than BZF itself. The Fe(II)/sulfite pretreatment alters the DBP formation potential, especially when Br⁻ is present. The formation of trichloromethane (TCM) is diminished following pretreatment with the Fe(II)/sulfite process, whereas a noticeable increase in the formation of dichloroacetonitrile (DCAN) is found. Moreover, Fe(II)/sulfite pretreatment enhances the formation of brominated DBPs. Therefore, special consideration should be given to DBP formation when a Fe(II)/sulfite system is employed as a pretreatment for the removal of BZF in water.

Graphical abstract